Really hard to tell in that picture. Scoopit out using a fine mesh strainer and dry it out on some paper towel. Might be more obvious that way.
There are times of the year when tiny flying insects swarm around the pool, die, and fall into the water. It looks like someone threw finely ground coffee onto the water’s surface. But if I scoop some out and look at it closely, it’s big parts (like wings, etc).